The Planets

The discovery of Pluto in 1930 set the limits of the known solar system, in which the nine planets orbitingthe sun present a fascinating series of enigmas.

Although there is a volcano on Mars, and Venus has giant plains of frozen lava, for many years it seemed that the planets' surfaces were geologically dead. But at the end of the seventies, living volcanoes spitting boiling sulphur, ice and frozen nitrogen were found on the moons of Jupiter and Neptune.

For centuries Jupiter, Saturn, Uranus and Neptune had puzzled astronomers, but in the late seventies the Voyager space probe embarked on a 12-year, four billion-mile journey to explore them, and found worlds that defied imagination.

For centuries human beings struggled to understand the origins of the Moon. But even after 20 years of lunar exploration, scientists were still in the dark. Then an astronomer from Arizona came up with a solution to the riddle.

The series on the history of the solar system continues with the story of man's quest to understand the body atthe centre of our solar system -the Sun -from the etchings made by Galileo to the very latest solar probes.

This week's film examines the astonishing weather systems found throughout the solar system. They include sulphuric acid rain, metallic snow and violent dust storms.

The series on the history of the solar system continues with a look at extra-terrestrial life. With the failure of the Viking probe to discover life on Mars in 1976, scientists gave up hope of finding alien life in our solar system. However, scientists are now becoming optimistic again of finding proof.

The series ends with a look at the fate of the solar system. Over the next four billion years, as a result of changes in the Sun. the Earth's oceans will boil, Saturn will lose its rings and one of Neptune's moons, Triton, will break apart to form a new ring system. Will the future of humankind depend on finding a solar system with a planet like Earth?